The treatment of certain diseases of the human body often requires the short-term or long-term infusion of drugs, blood products or nutritional or other fluids into the patient's venous or arterial system. While such fluids can be administered extracorporeally by transcutaneous injection, in some cases, as when a particular patient's regime requires repeated access for drug infusion, or where infection is of acute concern, it is desirable to provide the patient with a totally implanted infusion system.
Such a system includes an injection portal which is an infusate chamber implanted subcutaneously and placed on the chest wall or other convenient body location. The portal is fitted with a needle-penetrable septum which is located directly under the skin by which drugs or other fluids may be introduced into the portal by transcutaneous injection through the septum. The portal has a fluid outlet tube or stem which is connected to one end of a flexible catheter which leads to the infusion site which is usually a blood vessel or particular body cavity, e.g., the peritoneum. Since the system is completely implanted, it reduces the risk of infectious complications and allows drug infusion which is targeted to the specific patient malady. Even though the delivery system may be implanted for a long period, the patient remains ambulatory and can be treated on an out-patient basis and the system does not interfere with the normal daily activities of the patient.
A similar prosthesis can be used to draw blood from an artery or vein for blood sampling purposes.
Since an implantable device of this type may remain in the patient's body for many months, it is essential that the connection of the catheter to the portal remain secure and fluid-tight during the entire period of implantation. If the connection should fail or if there should be an infusate leak at that location, the infusate dose required to treat the patient which is injected into the portal will not be conducted to the targeted infusion site in the patient's body. Rather, some or all of the infusate will be dispensed at the site of the portal and could cause complications at that body location. In this connection, it should be appreciated that after a drug delivery system is implanted, the catheter is subjected to various stresses and strains due to movements of the patient's body, weight changes, etc. These are reflected in tensile and twisting forces at the connection of the catheter to the portal outlet which tend to upset the integrity of that union.
In an attempt to avoid this leakage problem and the attendant complications, various steps have been taken to strengthen the connection between the catheter and the portal. These include the providing of raised circular rings or ribs on the portal outlet stem over which the catheter wall is stretched. These lines of localized resilient engagement resist sliding movements of the catheter from the portal stem. In some systems, the connection is made somewhat more secure by providing a locking ring or bushing which encircles the catheter and is releasably captured on the catheter segment engaged on the portal stem by the raised ribs thereon.
We have found, however, that these prior catheter connections are not entirely satisfactory. Sometimes the tensile forces exerted on the catheter due to movements of the patient still suffice to separate the catheter from the portal or to tear the catheter at that point of connection because of a poor distribution of stresses on the catheter wall. Certain prior systems are disadvantaged in that it is quite difficult to connect the catheter to the portal outlet stem. This is because that stem is often very small (e.g. 1 mm OD), and to make the connection, the stem must be threaded into the end of the catheter lumen which is itself equally small. Furthermore, when inserting the portal stem into the catheter, if one is not quite careful, the catheter will be punctured by the end of stem which, being so small, constitutes a sharp point.
In addition, it should be kept in mind that it may be necessary to disconnect the catheter from an already implanted injection portal in the event that the catheter has to be replaced for one reason or another. For example, it sometimes happens that the catheter lumen becomes clogged by clots or other debris. Therefore, it is desirable that any connection between the catheter and the portal be separable from the portal with a minimum amount of effort and finger manipulation by the surgeon who must make that repair subcutaneously. The prior catheter connection systems of which applicant is aware, do not facilitate such ready connection and disconnection of the catheter to and from the portal.